DIELECTRIC-PROPERTIES OF SOILS IN THE 0.3-1.3-GHZ RANGE

In 1985, we reported the development of a semiempirical dielectric mod el for soils, covering the frequency range between 1.4 and 18 GHz. The model provides expressions for the real and imaginary parts of the re lative dielectric constant of a soil medium in terms of the soil's tex tural composition (sand, silt, and clay fractions), the bulk density a nd volumetric moisture content of the soil, and the dielectric constan t of water at the specified microwave frequency and physical temperatu re. This communication provides similar expressions for the 0.3-1.3-GH z range. Upon comparing experimental results measured in this study wi th predictions based on the semiempirical model, it was found that the model underpredicts the real part of the dielectric constant for high -moisture cases and underestimates the imaginary part for all soils an d moisture conditions. A small linear adjustment has been introduced t o correct the expression for the real part and a new equation was gene rated for the effective conductivity to correct the expression for the imaginary part. In addition, dielectric measurements were made to eva luate the dependence of the dielectric constant on clay type. The resu lts show significant variations for the real part and large variations for the imaginary part among soils with the same clay fractions but w ith clays of different specific surface areas.